1. Field of the Invention
The present invention relates to display systems and, more specifically, to a display system including a projector and a screen which are mounted on a vehicle so that the projector emits a light beam representing an image onto the screen.
2. Description of the Background Art
In recent years, there have been increasing needs to enjoy entertainment such as videos inside or around a vehicle irrespective of time and place. In order to fulfill such needs, the development of a vehicle-mounted display system in which a projector emits a light beam representing an image onto a screen has accelerated. Hereinafter, three examples of a conventional display system are described.
A first display system includes a projector and an interior screen which are mounted inside a vehicle, and an exterior screen which can be installed outside the vehicle. The projector is mounted on a ceiling of the vehicle so as to rotate approximately about the vertical axis. Specifically, if a viewer desires to watch a video on the interior screen, a projection lens of the projector is directed to the interior screen. On the other hand, if the viewer desires to watch a video outdoors by using the exterior screen, the projection lens is directed to the exterior screen.
In the first display system, however, the viewer has to install the exterior screen outside the vehicle before enjoying video. Moreover, the viewer also has to set the projector as required so that video is appropriately displayed on the exterior screen. In this way, the viewer is subject to burdensome operations whenever installing the exterior screen.
A second display system includes a projector and a screen which are mounted inside a vehicle. The projector is mounted typically on a ceiling of the vehicle. The screen reflects a light beam emitted from the projector, thereby presenting video to the viewer.
Generally speaking, however, vehicles have transparent windows which occupy a larger proportion of the inner space than those of airplanes or trains do. In other words, relatively more external ambient light enters inside the vehicle. Such external ambient light makes it difficult for the viewer to view the video presented by the second display system.
A third display system includes a liquid crystal display device mounted inside a vehicle and a half mirror. The liquid crystal display device is mounted near a center portion of a ceiling of the vehicle so that the display surface of the liquid crystal display device is oriented downward approximately in a vertical direction for displaying images. The half mirror is mounted below the liquid crystal display device so that the surface of the half mirror is positioned at an angle of 45 degrees with respect to the display surface of the liquid crystal display device. This half mirror reflects the images displayed by the liquid crystal display device to the back seat in the vehicle, and also allows light to pass therethrough. In the above-structured third display system, a viewer sitting in the back seat views the images reflected by the half mirror. Furthermore, since the half mirror also transmits light, the viewer sitting in the back seat can also view, through the half mirror, the situation ahead of the vehicle beyond the windshield of the vehicle (specifically, a sight and/or the state of traffic). Still further, a driver can check a rear portion in the vehicle or behind the vehicle by viewing images reflected by the room mirror through the half mirror.
According to the above-structured third display system, emitted light (that is, images) from the liquid crystal display device is directed to the surface of the half mirror at an angle of incidence of approximately 45 degrees. Furthermore, with the reflective characteristic of the half mirror, approximately half of the incident light is reflected to the back of the vehicle, and the remaining half to the bottom thereof. With a combination of the liquid crystal display device and the half mirror described above, the viewer sitting in the back seat views virtual images of the images displayed on the liquid crystal display device through the half mirror.
In the third display system, however, even when the viewer sitting in the back seat does not want to see images, the half mirror is always located in front of the viewer, thereby detrimentally affecting the comfort of the viewer in the vehicle.